14 DAY TRIAL // According to the conclusions of a new study by researchers at the Rockefeller University in New York, it would appear that the human nose is capable of distinguishing between 1 trillion different smells, or odors. This discovery casts a shadow on previous estimates, which held that the nose was only able to tell apart roughly 10,000 smells.
The difference between the new investigation and previous results is several orders of magnitude, researchers report in a paper published in the March 20 issue of the top journal Science. Interestingly, very few studies have been conducted to test the maximum sensory capabilities of the human nose.
Scientists working in this area have suspected for a long time that this organ is capable of identifying a very large number of smells, but evidence to back up this claim has been lacking. The nose “has just been sitting there for somebody to do,” explains Rockefeller olfactory researcher and study co-author Andreas Keller.
For the new experiments, scientists mixed sets of 10, 20, or 30 odorous molecules, selected from a bank of 128 chemicals. Each mixture shared several molecules with other mixes, and researchers asked 26 participants to smell all of them. The goal was for test subjects to identify the substances that smelled differently despite their commonalities.
The team found that participants had no trouble discriminating between different mixtures as long as the molecular components in each did not overlap by more than 51 percent. In other words, if more than half of the constituents in the solution were the same, telling them apart became very difficult.
Determining the number of scents the human nose could perceive then became a simple issue of calculating the possible molecular combinations that overlapped by less than 51 percent. The team found more than 1 trillion potential combinations that the human nose should theoretically be able to detect, Nature News reports.
This high figure casts a new light on the importance of understanding the mechanisms that link how the nose and the brain work together to process smells and related sensations. These processes are not very well understood, even though scientists have been trying to figure them out for decades.
“It’s hard to organize odors,” says New York University School of Medicine olfactory researcher Donald Wilson. The human nose features roughly 400 different types of scent receptors, but “the relationship between the number of odorants that we can discriminate and the number of receptors that we have is unclear,” says Weizmann Institute of Science neuroscientist Noam Sobel.
This investigation is one of the most important for revealing that humans do not actually have such a bad sense of smell, as many scientists have argued based on previous results.